This invention relates to a fuel injection system for an internal combustion engine, and more particularly to a fuel injection system which is adapted to use, as a power supply therefor, a generator driven by an internal combustion engine, to thereby feed a fuel to the internal combustion engine.
An internal combustion engine which has been used in the art generally employs, for the purpose of accurately controlling feed of fuel thereto, a fuel injection system which includes an injector for rendering a needle valve open to inject fuel therethrough while a driving current or exciting current is being fed thereto and a circuit for controlling the injector. In such a fuel injection system, a battery arranged in a vehicle, a ship or the like in which the internal combustion engine is mounted is generally used as a power supply for drive, as seen in, for example, U.S. Pat. No. 4,690,118.
Recently, it has been desired to apply such a fuel injection system to an internal combustion engine used for an equipment in which no battery is mounted such as an outboard motor or the like as well. In this instance, a generator mounted on the internal combustion engine would be used as a power supply for the fuel injection system.
Use of a generator as a power supply for the fuel injection system permits feeding of fuel to the engine to be smoothly accomplished, so long as the engine speed is sufficiently increased and the generator generates an enough output. However, when the engine speed does not fail to be increased to such a sufficient level and the output of the generator is kept at a low level, a voltage applied to a switch control circuit for controlling a switching circuit adapted to control an exciting current flowing through an exciting coil of the injector is reduced below a level which renders operation of the switch control circuit possible, resulting in the switching circuit being often interrupted. Such interruption of the switching circuit causes the injector to stop fuel injection, so that the amount of fuel fed to the engine is insufficient, to thereby render operation of the engine at the time of a low engine speed, particularly, at the time of starting unstable.